Application Report
Why is Galvanic Compatibility Important
to Your Broadband Network Integrity?
In high school chemistry class you learn about different
elements—how those elements have various charge levels
and how electrons and protons jump from one element to
another when they are in proximity to each other.
Most people never truly recognize what this means in real life.
A perfect example of this is rust. Oxygen reacts with iron and its
alloys in the presence of water and other pollutants in the air and
the result is rust, a red substance that ends up causing the eventual
decay of the iron. While this is an example of oxidation, this reaction is similar in nature to galvanic corrosion. Galvanic corrosion is
the corrosive effect of two metals instead of a metal and oxygen.
In marine applications a sacrificial metal such as zinc is used as
an anode to protect other metals (cathode) such as iron or steel
that are more critical from corroding. The zinc corrodes much faster
because of the voltage generated by the dissimilar metal effect
(see Anodic index chart).
The greater the voltage difference between two metals, the higher
potential for corrosion between these two metals.
Now, flash forward to your broadband network. Various metals
come in contact throughout your network, but one of the most
critical areas that you do not want to corrode is at your bonding
point. The National Fire Protection Agency Association requires
that your broadband network be properly grounded to prevent
voltage spikes, fires and other property damage. Broadband
system operators have standardized on annealed solid copper
or Copper Clad Steel (CCS) products for the bond wire.
But one area sometimes overlooked is the actually bonding apparatus. Many bonding product suppliers promote ground block
products that use various metals such as zinc, aluminum or stainless
steel; however the basic materials in the network are copper. The
F-Connector used in the CATV space has primarily been standardized on brass (primary element is copper) and the bond wire is
copper or CCS. So the obvious question is if galvanic compatibility or dissimilar metals cause corrosion and potential signal integrity
issues, why wouldn’t you protect the integrity of your subscriber
using a copper based bonding apparatus?
A brass connector mating to a non-brass interface will begin to
corrode. This corrosion may take months or years, but the basic
metal-to-metal interface will corrode. A non-brass interface to
the bond wire will face the same corroding effect as the connector to the non-brass interface. What does this really mean?
This corrosion, over time, builds up contaminants and these
contaminants interfere with the signal propagation through these
interfaces. This will be seen in the increase of the resistance from
the Connector to the bonding apparatus, or the bonding wire
or both. The American National Standard from the Society of
Cable Telecommunication Engineers (ANSI/SCTE 129 2007)
states that after 1000 hrs of Salt Spray, the grounding interface
must maintain < 50 milliohm resistance between the device and
the bond wire.
As these interfaces corrode and the resistance increases, you
begin to lose your path to ground. A simple rule of thumb is that
www.commscope.com
Figure 1
a signal will take the path of least resistance to ground. This may
have been through your bonding device on day 1, but now as
the corrosion and the resistance increases, it may be back at the
tap, or in the home at the back of a television or set top box.
These various ground points may not be adequate to shunt electrical noise interference from in-home sources such as refrigerators
and microwaves or external sources such as electrical storms and
surges to ground. The in-home network may distribute this noise
back toward the network as shown in Figure 1.
This noise may take one of several forms. It may be random or
discrete ingress from external sources, and it may be common
path distortion generated by the non-linear effects of the corrosion
itself. Once the noise begins to funnel back toward the network, it
will be combined both as interfering ingress and as thermal noise
and will be amplified multiple times before eventually making its
way back into the headend cable modem termination system
controllers. Once noise makes it into the signal path it is very difficult to filter out since it is now occupying the same bandwidth as
your intended signaling and can significantly reduce the Signal-toNoise performance of your system.
compacted brass. The dense brass body and our nickel plating
resist corrosion from external influences like moisture and pollution.
The brass itself is made up primarily of copper, the same copper
found in the brass F-Connectors and the annealed solid copper
or CCS bond wire. From the Anodic index chart, brass and pure
copper have an Anodic voltage delta of less than +/-0.15V
which meet the MIL-STD-889 for suitable in a harsh outdoor
environment. All CommScope brass ground blocks use our 7/16
split bolt to provide a large contact area to the bond wire and the
ability to exert a measurable torque onto the bond wire without
twisting or tearing into the copper.
How can this be prevented?
One easy way to prevent this basic corrosion is to match your
galvanic materials together. CommScope has provided a copper based solution for many years with their solid brass line of
Ground Blocks. These products were developed specifically with
your broadband network in mind to provide the ultimate corrosion
resistance and leading lightning suppression capability. These
ground blocks are made from forged brass. This is very densely
1100 CommScope Place, SE • P.O. Box 1729 • Hickory, North Carolina 28603
Tel 1.800.982.1708 or 828.324.2200 • Fax 828.328.3400 • www.commscope.com
©2012 CommScope, Inc . All Rights Reserved • B-TD-HC-1 • 03.12
Why chance your network integrity with bonding blocks made
from other metals or even multiple metals when you can make
a clear informed decision and standardize on a true solid brass
design?
For more information on these grounding products, please visit
www.commscope.com or CommScope’s eCatalog.
www.commscope.com